1. Field of the Invention
The present invention relates to a clamping apparatus for an injection molding machine provided with a stationary platen, and a movable platen capable of moving along tie bars.
2. Description of the Related Art
Generally, a mold clamping apparatus for an injection molding machine has a stationary platen fixed to a frame, a plurality of tie bars each having one end fixedly held on the stationary platen, and a movable platen supported on the tie bars for movement along the same. A support member, which is called a rear plate or a link housing depending on its morphology, is disposed on the frame on the opposite side of the stationary platen to support the other ends of the tie bars, and to hold a driving mechanism for opening, closing and clamping a mold.
In a clamping apparatus provided with a toggle joint for pressing a movable mold against a stationary mold, the parallelism of the support member with respect to the stationary platen must accurately be adjusted when adjusting die height. Because errors made in assembling the clamping apparatus and the abrasion of pins connecting the links of the toggle joint lead directly to the deterioration of close contact between the stationary mold and the movable mold.
A parallelism adjusting mechanism for adjusting the parallelism of the support member with respect to the stationary platen is disclosed in JP B2 285/1996 issued to the assignee of the present invention. This prior art parallelism adjusting mechanism has a support member referred to as link housing and provided with adjusting gears each having a threaded bore and linked to the threaded end sections of the tie bars. The adjusting gears are driven by a single motor mounted on the link housing. A plurality of spur gears are supported within the link housing to transmit the driving force of the motor to the adjusting gears. One of the gears of a gear train for transmitting the driving force to each adjusting gear can be engaged with and disengaged from the adjacent gears. This prior art parallelism adjusting mechanism is capable of adjusting die height in a high accuracy by the single motor.
This prior art parallelism adjusting mechanism, however, needs some improvements. For example, torque acting on the gear must be removed when disengaging the same from the adjacent gears, the gears must properly be positioned relative to each other when engaging the gear with the adjacent gears. Accordingly, he automatic adjustment of die height requires complicated control operations. Since he gearing are built in the link housing, the parallelism adjusting mechanism requires difficult maintenance work. It is difficult to form the parallelism adjusting mechanism in a compact construction because an appropriate stroke must be secured for a cylinder actuator for engaging the gear with and disengaging the same from the adjacent gears, and the motor for driving the gears and a cylinder actuator for driving the toggle mechanisms protrude from the link housing.